Demosthenes mentions a law that set an expiration-date of one year for any probouleuma that was not voted on by the Assembly (Dem. 23.92). The circumstances of this piece of evidence, however, and the way Demosthenes mentions it, are confusing. A man named Aristocrates, while serving as Councilor, had moved a probouleuma in the Council, awarding honors on a man named Charidemus (Dem. 23.90). Later, Demosthenes wrote a speech prosecuting Euthycles on a charge of γραφὴπαρανόμων, or “illegal proposal” (Dem. 23.100). In his speech, Demosthenes anticipates the kinds of arguments Aristocrates might use to defend himself. At one point, Demosthenes says: “I imagine that he will use the following argument, and that he will try very hard to mislead you on this point. The decree, he will urge, is invalid because it is merely a Preliminary Decree (προβούλευμα) and the law provides that votes of the Council shall be in force for one year only; therefore, if you acquit him today, the commonwealth can take no harm in respect of his decree.” (Dem. 23.92). In other words, Arisocrates will try to argue that he cannot be prosecuted for making an illegal motion, since the motion he made more than a year ago is no longer in force.

If we can take this as evidence, then it seems that under certain circumstances a probouleuma would fail to come up for discussion for more than a year after the Council passed it, and it would then expire.